The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
Nowadays Ultra High Frequency (UHF) tags are commonly used in timing systems for large sports events e.g. mass sports events for running, cycling or motorcycling. UHF tags are cheap, low weight, and can be read fast and from relatively large distances. When a tag comes within the radiation field of the antenna mat, the tag starts sending out ID messages as a result of activation by the radiation field. The antennas in the mat receive these messages and transfer the messages to a decoder (an analyser). The decoder is connected to the antenna mat and is programmed to determine the passage time of the tag with a unique ID on the basis of the signal strength of the received messages. Because the electromagnetic field produced by the antenna in the mat is strongest above the center of the mat, it is possible to determine the point in time when the tag passes the antenna with reasonable accuracy.
Although the current state of the art mat-based timing systems provide highly reliable timing results with more than 99.9% up to 100% reliability for mass sports events, these mat-based timing system have some disadvantages. For example, installing the timing system requires putting the mat elements of a main mat and, possibly, one or more back up mats, in place and testing it. This process requires blocking the track for some time which may interfere with the organisation of the sports event. This is particular inconvenient in mass sports events such as a marathon or the like. Further, although a mat is modular and each mat element is made of a lightweight material, the total weight of the mat elements forming a full finish line may be substantial.
Further, when athletes pass the antenna mat they may step onto the mat, which may cause forces applied to the mat which may be considerable especially when large amounts of athletes cross the mat at once. These forces may influence the antenna performance due to detuning effects. Moreover, the forces may also induce friction between the mat elements which may influence the HF connection that connects the mat elements to the decoder. Additionally, in some sports like cycling the mats may hinder the athletes upon passing. In other sports the conditions are either not suitable for using a mat such as mud runs or ice skating.
Instead of a mat antenna, side antennas could be used in order to circumvent at least some of the above-mentioned problems. Timing systems using portable side antennas are known in the art. Such side antenna is typically configured as a flat RFID antenna connected to a tripod support structure, which fixates the antenna at a predetermined height from the ground. Such side antennas however have some disadvantages. For example, unlike the mat antenna configuration, in a side antenna configuration athletes may hinder the reading of other athletes. This is because signals in the UHF spectrum, e.g. between 0.8 and 2.4 GHz are easily absorbed or at least attenuated by the human body, in particular the torso. Hence, in a side antenna configuration, athletes located between the antenna and a passing athlete may hinder the activation and/or reading of the tag of the passing athlete, thus leading to errors in detecting passing athletes.
Furthermore, in timing systems the antennas of the RF antenna structures require accurate positioning with respect to the track in order ensure high reading rates, or at least reading rates that match the specifications of the timing system. In contrast to mat antennas (in which the alignment and positioning of the antenna elements can be easily controlled by sideway alignment of the mat elements) aligning and positioning side antennas in such a way that the read rate is optimal is more difficult. The side antennas need to be positioned and configured such that a radiation field of sufficient dimensions and power is generated across a track. For these reasons, up till now, timing systems based on side antenna's that are suitable for timing mass events with a reliability that match the current state of the art mat-based did not exist.